These days a resin tube is increasingly being used as an automotive fuel tube. A resin tube has many advantages: Unlike a metal tube, a resin tube does not rust and is easy to process. In addition, a resin tube is lightweight and enables a high degree of design freedom.
On the other hand, there is a problem in the use of a resin tube as a fuel tube: Gasoline can permeate the tube and leak out. From an environmental standpoint, regulations on the fuel permeability of a resin tube for use as a fuel tube are becoming increasingly stricter these days in the United States and Europe.
The fuel permeability of a resin tube for use as a fuel tube can be determined by measuring a hydrocarbon permeability in accordance with CARB DBL test method using a SHED test machine; and a resin tube is determined to be low fuel-permeable when the measured hydrocarbon permeability is not more than 50 mg/m·day.
To impart a fuel permeation-resistant property (hereinafter referred to as “low permeability”) to a resin tube for use as a fuel tube is therefore an urgent problem to be solved. A low-permeability multilayer resin tube is known which comprises a low-permeability resin layer in the innermost layer to be in contact with gasoline and a layer of a polyamide resin or the like in the outermost layer, with an adhesive layer interposed therebetween. A fluororesin (ETFE) is known to be very excellent in the low permeability, and the development of a resin tube comprising a barrier layer of the fluororesin is now in progress.